The present invention relates to a measuring apparatus based on the bioelectrical impedance method, and in particular, to an improved circuit configuration of the apparatus constructed using an integrated circuit so as to be capable of measuring bioelectrical impedance.
An apparatus has been conventionally suggested and provided, which estimates a factor concerning to a body constitution based on the bioelectrical impedance method. There has been used, for example, a body fat meter which measures a bioelectrical impedance value of a living body of test subject by applying a current through end portions of the body of the test subject and measuring a voltage value between the portions of current application, and estimates a body fat rate from the measured value as well as a set of body data of the test subject including height, weight and sex, taken into account. An internal circuit of this body fat meter has been made up with a plurality of components including a microcomputer served as a control and processing unit (CPU), an operational amplifier, or the like.
The microcomputer employed in the above body fat meter has no functions other than those for the general microcomputer such as control and processing function, input/output ports or the like, leaving the other components to be arranged out of the microcomputer, connected thereto and controlled through respective ports.
In the body fat meter of the prior art, an alternating current generator section for generating an alternating current to be applied into a living body and outputting it therefrom, a differential amplifier for amplifying an analog signal outputted from the living body, an A/D converter for converting the analog signal from the differential amplifier to a digital signal, and the likes are entirely composed of a plurality of components arranged out of the microcomputer. Owing to this, sufficient amount of man-hour has to be used for mounting those components onto the circuit board. Further, disadvantageously the substrate of the body fat meter has necessarily increased in size, thus causing a negative effect that prevents the downsizing of the body fat meter itself.
Still further, since the analog signal obtained from the living body is inputted to, outputted from and processed by the differential amplifier and the A/D converter, which are connected via wiring patterns on the substrate, the signal is likely to be subject to interference by noise entering through the wiring patterns, resulting in an error in measuring of the bioelectrical impedance which otherwise should have been measured accurately.
Yet further, the body fat meter is often used in the relatively humid atmosphere such as in a bathroom or in a rest room, and sometimes the circuit board absorbs humid resulting in change of the dielectric constant, which may also cause an error in measuring the bioelectrical impedance. Accordingly, a level of accuracy in measurement of the bioelectrical impedance has been retained by taking such counter measure as employing a substrate with better humid-resistive characteristics to solve the problem of humidity.
Further disadvantageously, especially in such a body fat meter that is required to increase the number of measuring electrodes to increase the number of sites to be measured, or that is required to vary an alternating current applied into a living body to measure the bioelectrical impedance at a plurality of frequencies, a circuit configuration necessarily becomes more complicate and larger in size, which makes it much more difficult to downsize the body fat meter.
The present invention is made in the light of these problems described above and the object thereof is to provide a bioelectrical impedance measuring apparatus of high precision with low price, which has fewer number of circuit parts to reduce the number of manufacturing processes and thereby to reduce the cost therefor, and to provide a body fat meter employing said apparatus.
According to an aspect of the present invention, a bioelectrical impedance measuring apparatus for measuring a bioelectrical impedance of a test subject based on the bioelectrical impedance method, comprises an input device, an alternating current signal generating device, a switch, an amplifier, an analogue-to-digital converter, a control and processing device, a storage unit, an output device, and an oscillator, in which:
said input device inputs a personal body data of the test subject;
said alternating current signal generating device generates an alternating current signal to be applied to a living body;
said switch switches a connection to an electrode for measuring a voltage of the living body and that to a reference impedance to each other;
said amplifier amplifies a measured alternating voltage signal;
said analog-to-digital converter converts an analog value representative of amplified alternating voltage signal to a digital value;
said control and processing device estimates a factor concerning to a body constitution of the test subject based on the inputted personal body data and a measured bioelectrical impedance value, and controls each device;
said storage unit stores the inputted personal body data, the estimated factor concerning to the body constitution of the test subject, or the like;
said output device outputs a signal for indicating a set of estimated data concerning to the body constitution; and
said oscillator generates a clock signal to actuate the control and processing device;
wherein said apparatus has a microcomputer including said alternating current signal generating device, said switch, said amplifier, said analog-to-digital converter, said control and processing device, said storage unit, said output device, and said oscillator integrated into a circuit on a one-chip.
A microcomputer employed in the bioelectrical impedance measuring apparatus according to the present invention further includes a divider and a frequency switching device, in which:
said divider generates an alternating current signal of multi-frequency; and
said frequency switching device selectively outputs the alternating current signal of multi-frequency generated by said divider;
wherein both of said devices are also integrated into said circuit on said one-chip.
A microcomputer employed in the bioelectrical impedance measuring apparatus according to the present invention further includes a switch and another switch, in which;
said switch is connected to a plurality of power supply electrodes for measuring a bioelectrical impedance disposed out of said microcomputer, and switches alternating current signals from said alternating current power supply to output the signal therefrom; and
said another switch is connected to a plurality of voltage detection electrodes disposed out of said microcomputer, and switches alternating voltages to be measured;
wherein both of said switches are also integrated into said circuit on said one-chip.
A microcomputer employed in the bioelectrical impedance measuring apparatus according to the present invention further includes a constant voltage generating device, a low voltage detecting device, a constant voltage supply device, a sensor input switching device, an amplifier; a converter, in which:
said constant voltage generating device is connected to a power supply disposed out of said microcomputer and generates a constant voltage;
said low voltage detecting device determines whether or not the level of voltage of said power supply disposed out of said microcomputer is on or over a specific level;
said constant voltage supply device supplies the constant voltage to a sensor disposed out of the microcomputer;
said sensor input switching device switches signals from the sensors disposed out of the microcomputer;
said amplifier amplifies an output signal from said sensor input switching device; and
said converter converts an analog value representative of said amplified output signal to a digital value;
wherein all of said devices are also integrated into said circuit on said one-chip.
Further, said alternating current signal generating device comprises a storage unit, an output device, and a converter, in which:
said storage unit stores a sine wave voltage value;
said output device outputs a voltage signal based on said sine wave voltage value stored in said storage unit for each input of clock signal; and
said converter converts a voltage signal to a current signal.
Further, said analog-to-digital converter comprises a calculator which calculates a digital value for every clock signal during a sampling period and measures an alternating voltage waveform to calculate an alternating voltage effective value.
Further, said alternating current signal generating device comprises a low pass filter and a voltage-to-current converter, in which:
said low pass filter removes high frequency components from an alternating square wave voltage outputted from said divider to convert it into a sine wave voltage; and
said voltage-to-current converter converts said sine wave voltage to said alternating current signal to be applied to the living body.
Further, said analogue-to-digital converter comprises a rectifier, a filter circuit and a calculator, in which:
said rectifier rectifies the alternating voltage signal amplified by said amplifier;
said filter circuit makes said rectified alternating voltage signal be an effective value; and
said calculator calculates a digital value from said signal made into effective value for each clock during sampling period.